6

This question already has an answer here:

I would like to have commands for left- and right gauss brackets which have a double vertical line, but otherwise behave exactly like \lfloor and \rfloor. In particular, they should come in various sizes and other things should stay unchanged.

I found two candidates, which are both not optimal, unfortunately:

  • \llfloor and \rrfloor in the package stmaryrd. Unfortunately they do not understand preceeding \left and \right commands. My impression is they are fixed size.

  • \lFloor and \rFloor in the package nath. They come in different sizes, but the problem is that including the package nath introduces automatic sizing behaviour of all symbols of parantheses-type. This might be interesting, but for the moment this change is just too radical for my taste.

marked as duplicate by JouleV, Dox, Andrew Swann, Raaja, Stefan Pinnow Mar 19 at 8:55

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5

Thanks to Werner for providing a solution for this similar question.

A rather quick fix using scalerel would be the following.

Conveniently, scalerel provides \scaleleftright[<max width>]{<left obj>}{<stuff>}{<right obj>} (and a comparable \stretchleftright) for scaling/stretching both <left obj> and <right obj> to the height of <stuff> (constrained, if required and optional, to a width of <max width>). Here's a quick example:

\documentclass{article}
\usepackage{scalerel, stmaryrd} % http://ctan.org/pkg/scalerel

\newcommand{\gaussbracket}[1]{\stretchleftright{\llfloor}{#1}{\rrfloor}}

\begin{document}
\[ \gaussbracket{\displaystyle\sum_{i=1}^n i} \]
\end{document}
  • 1
    Very very good. I have really appreciated your code. – Sebastiano Mar 18 at 21:55
  • Thanks, but it's not exactly what I wanted. I wanted a pair of commands, one for left and one for right bracket, which can be resized by \big, \Big, etc. Also, the scaled symbol does not look so good (too thick vertical line). – azimut Mar 18 at 23:31
  • @azimut. I think the linked question would be an interesting read then, I wouldn't know how to make a non extensible delimiter extensible. – Peiffap Mar 19 at 6:32
5

An option if you don't want to use any packages other than amsmath would be to place two \lfloors next to each other with a little negative space between:

enter image description here

This has the advantage of not thickening the horizontal portion of the delimiter.

\documentclass{article}
\usepackage{amsmath}

\newcommand{\gaussbr}[1]{%
    \left\lfloor\hspace{-.33em}\left\lfloor #1\right\rfloor\hspace{-.33em}\right\rfloor%
    }

\begin{document}

\[
\gaussbr{A}\gaussbr{\sum_{n=0}^{\infty}a_n}
\]

\end{document}

Of course, you can adjust the amount of negative space to your liking.

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